Novel reporter constructs for compound screening

ABSTRACT

The instant description provides reporter constructs, transgenic cells, and transgenic organisms and methods for identifying agents that can regulate gene expression and improve performance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application 61/347,516, filed on May 24, 2010. The application also claims priority to the PCT application PCT/US10/45941, filed on Aug. 18, 2010. The entire contents of each of these applications are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to reporter constructs, transgenic cells and transgenic organisms that can be used for the identification of agents that regulate gene expression.

BACKGROUND OF THE INVENTION

Manipulation of organisms or in vitro cultures to alter and/or improve phenotypic characteristic often requires the modulation of gene expression. For example, the stress tolerance of a plant can be improved through modifying the expression of genes involved in signal transduction pathways related to various stress responses. One way to achieve this goal is to genetically engineer the organisms or in vitro cultures, an approach that is costly and time consuming. An alternative approach is to identify chemical compounds that can be applied to these organisms, e.g., plants, mammals, yeast, Drosophila, C. elegans, or bacteria etc., or their in vitro cultures to obtain the desired phenotypes. Currently, chemicals are screened through reporter constructs in which a reporter polynucleotide is directly fused to a promoter sequence that is capable of being recognized by a transcriptional regulatory protein, i.e., proteins that can regulate the signaling pathways that contribute to the development of a desired trait. However, this conventional approach has limited sensitivity that leads to inefficient compound screening and/or requires significant effort to identify reporter cell lines or organisms suitable for the screen, i.e., reporter cell lines or organisms in which the function or expression of the transcriptional regulatory protein can be altered directly or indirectly in response to a compound treatment so that the amount of the resulting reporter molecule is readily discernible from the controls.

The present specification provides, inter alia, novel vectors, cell lines, and methods useful for modulating gene expression, identifying and analyzing regulatory sequences, and discovering new targets and reagents for improving plant performance or therapeutic intervention in human disease. The reporter constructs of the specification contain arrangements of additional genetic elements that can optimize the signal-to-noise ratio of the conventional promoter-reporter assay, minimize the efforts on characterization and development of reporter lines, and thus improve the sensitivity and the efficiency of the screens. These novel constructs and methods can also be used in a high-throughput format to identify agents that can be rapidly deployed induce modified gene expression and/or desired phenotypic alterations in organisms, for example, compounds can be applied to plants through a spray or via irrigation.

Examples of how to employ these reporter constructs and transgenic cells and organisms to identify useful chemical compounds are provided. Other aspects and embodiments of the specification are described below or can be derived from the teachings of this disclosure as a whole.

SUMMARY OF THE INVENTION

The present description provides a novel series of constructs, transgenic cells, transgenic organisms and methods which permit the identification of novel sequences and agents that are capable of modulating gene expression.

In one aspect, the present description provides a transcriptional fusion reporter system where a reporter gene construct comprises, in operable linkage, a target promoter sequence that can be recognized by a transcription regulatory protein, a polynucleotide sequence that encodes a DNA sequence-specific transactivator, and a reporter gene. The reporter gene expression is regulated by both the target promoter and the DNA sequence-specific transactivator.

In another aspect, the instant description provides a translational fusion reporter system where a reporter gene construct of the invention comprises, in operable linkage, a polynucleotide encoding a DNA sequence-specific transactivator and a polynucleotide encoding a translational fusion of a reporter molecule and a polypeptide of interest. The DNA sequence-specific transactivator regulates the expression of the translational fusion protein.

The DNA sequence-specific transactivator of the reporter gene construct of the invention contains at least a DNA binding domain and a transcription activation domain, for example, LEXA:GAL4, SEQ ID NO: 4 (a translational fusion of the DNA binding domain of LEXA and the activation domain of GAL4), or GAL4:VP16, SEQ ID NO: 28 (a translational fusion of the DNA binding domain of GAL4 and the transcription activator protein VP16).

In some embodiments, the DNA sequence-specific transactivator is a steroid-inducible transactivator, which regulates transcription when bound by a steroid, for example, LEXA:GAL4:GR, SEQ ID NO: 2 (a translational fusion of the DNA binding domain of LEXA, the activation domain of GAL4, and the ligand binding domain of glucocorticoid receptor), or GAL4:VP16:GR, SEQ ID NO: 7 (a translational fusion of the DNA binding domain of GAL4, the transcription activator protein VP16, and the ligand binding domain of glucocorticoid receptor). These transactivators remain in the cytoplasm until they bind dexamethasone, a glucocorticoid receptor agonist. The dexamethasone bound transactivators then translocate into the nucleus and activate the expression of a target protein, e.g. a reporter, a translational fusion of a reporter molecule and a polypeptide of interest, or a transcriptional regulatory polypeptide that regulates the expression thereof.

In some embodiments, the reporter gene construct comprises a dual-two component reporter system where a steroid-inducible DNA sequence specific transactivator, such as GAL4:VP16:GR (SEQ ID NO: 7), binds a steroid, for example, dexamethasone, and activates the expression of a transcriptional regulatory polypeptide that recognizes a target promoter sequence operably linked to a polynucleotide that encodes an additional DNA sequence-specific transcriptional activator, for example, LEXA:GAL4 (SEQ ID NO: 4). A reporter molecule or a fusion protein of a reporter molecule and a polypeptide of interest would be expressed from a promoter that can be recognized by said DNA sequence-specific transcriptional activator, for example, the opLexA promoter (SEQ ID NO: 5).

The reporter molecule of the instant description can be any reporter gene molecule, for example, reporter gene molecules or reporter polynucleotide whose expression or activity can be measured by calorimetric, fluorescent or luminescence signals, such as green fluorescent protein (GFP), luciferase (LUC), chloramphenicol transferase (CAT), and glucuronidase (GUS).

In another aspect, the instant description provides transgenic organisms or cells derived therefrom, such as microbes, mammals, yeast, Drosophila, C. elegans, which are transformed with the reporter gene constructs as described above.

In yet another aspect, the instant description provides methods of identifying chemical compounds comprising the steps of contacting at least one test compound with a cell that was transformed with any one of the reporter gene constructs as described above, and selecting a compound that alters the reporter gene activity relative to controls.

The instant description also provides compounds identified in accordance with the methods.

The instant description also provides methods to enhance plant performance by applying the identified compound to plants.

BRIEF DESCRIPTION OF THE SEQUENCE LISTING AND DRAWINGS

The Sequence Listing provides exemplary polynucleotide and polypeptide sequences of the instant description.

Incorporation of the Sequence Listing.

The copy of the Sequence Listing, being submitted electronically with this patent application, provided under 37 CFR §1.821-1.825, is a read-only memory computer-readable file in ASCII text format. The Sequence Listing is named “MBI-0096PCT_ST25.txt”. The electronic file of the Sequence Listing was created on May 23, 2011, and is 76,901 bytes in size measured in MS-WINDOWS. The Sequence Listing is herein incorporated by reference in its entirety.

FIGS. 1-9 depict reporter assay systems that can be introduced into an organism or a cell by transformation. The resulting transgenic organism or cell can be employed to identify useful chemistry that regulates a signaling pathway of interest. Ovals represent the polypeptides, rectangles represent polynucleotides, and hexagons represent one or more chemical compounds. Lines with arrow-heads indicate a direct or indirect chemical enhancement of activity whereas blunt-ended lines indicate a direct or indirect repression of activity by a chemical compound. Filled circles represent dexamethasone. FUSION represents a translational fusion of a polypeptide of interest and a reporter molecule, or its encoding polynucleotide. DBD:AD represents a translational fusion of a DNA binding domain (DBD) and a transcriptional activation domain (AD), or its encoding polynucleotide. DBD site is a promoter sequence which is bound by the DBD. REPORTER is any fluorescent, colorimetric or luminescent reporter, e.g. GFP (SEQ ID NO: 8), GUS (SEQ ID NO: 9), or luciferase (SEQ ID NO: 10), or a polynucleotide that encodes any of the aforementioned reporters. prTARGET represents a promoter can be recognized by a transcriptional regulatory polypeptide in the instant description. PROMOTER represents any promoter sequence. Roman numerals represent the serial events that may occur associated with the treatment of the chemical compounds. DBD:AD:GR represents a dexamethasone-inducible transactivator that encodes a translational fusion of a DNA-binding domain (DBD), a transcriptional activation domain (AD) and the ligand binding domain of the glucocorticoid receptor. DBD can be any DNA binding domain, for example, the DNA binding domain of GAL4, SEQ ID NO: 18, or the DNA binding domain of LexA, SEQ ID NO: 16:AD represent any transcription activation domain, for example, the activation domain of GAL4, SEQ ID NO: 20; VP16, SEQ ID NO: 22; EDLL, SEQ ID NO: 23-26.

FIG. 1. Transcriptional fusion assay system I: i) transcription and translation of a DNA sequence-specific transcriptional activator DBD:AD:GR; ii) translocation of the DNA sequence-specific transcriptional activator into the nucleus upon addition of dexamethasone, and binding to its cognate promoter sequence DBD site; iii) transcription and translation of the reporter (reported); iv) transcription and translational of a transcriptional regulatory polypeptide leads to v) binding of the transcriptional regulatory polypeptide to its target promoter sequence; vi) modulation of the transcriptional regulatory polypeptide binding or activation by a compound through direct or indirect mechanisms; vii) transcription and translation of the reporter (reporter2).

FIG. 2. Transcriptional fusion assay system II: i) compound-mediated induction or repression of DBD:AD transcription under the regulatory control of a promoter recognized by a transcriptional regulatory polypeptide; ii) transcription/translation of DBD:AD; (iii) binding and activating the DBD site promoter; (iv) transcription/translation of the reporter gene.

FIG. 3. Transcriptional fusion assay system III: i) transcription and translation of DBD1:AD1:GR; ii) translocation of DBD1:AD1:GR into the nucleus with binding to the DBD1 site upon the addition of dexamethasone; iii) transcription and translation of the reporter (reported); iv) transcription and translational of the target transcriptional regulatory polypeptide, which leads to v) binding of the transcriptional regulatory polypeptide to the target promoter sequence; vi) modulation of transcriptional regulatory polypeptide binding or activation through direct or indirect mechanisms by a chemical compound; vii) transcription/translation of DBD2:AD; viii) binding of DBD2: AD to the DBD2site promoter; ix) transcription and translation of the reporter (reporter2).

FIG. 4. Translational fusion assay system I.: i) transcription/translation of DBD:AD; ii) binding to and activation of the DBD site promoter; iii) transcription/translation of the fusion protein comprising of a reporter molecule and a polypeptide of interest; iv) stabilization or degradation of the fusion protein upon the treatment of chemical compounds.

FIG. 5. Translational fusion assay system II. Two rounds of amplification. i) transcription/translation of DBD1:AD; ii) binding to and activation of the DBD1 site promoter; iii) transcription/translation of a second DNA sequence-specific transcriptional activator DBD2:AD; iv) binding and activating the DBD2 site promoter; v) transcription/translation of the fusion protein comprising of a reporter molecule and a polypeptide of interest; vi) stabilization or degradation of the fusion protein upon the treatment of chemical compounds.

FIG. 6. A two-component transcriptional fusion system of the instant description showed increased signal-to-noise ratio compared to a one-component transcriptional fusion system. Cell lines transformed with A (a direct promoter GFP transcriptional fusion), i.e., “Z27379”, and cell lines transformed with B (a two-component transcription fusion reporter system II), i.e., “Z164567”, “Z164569”, “Z164571”, “Z164572”. “Z164577”, “Z164578”, “Z164581”, “Z164583”, “Z164588”, “Z164589”, were subjected to an induction treatment, which activates the prTarget promoter (black columns), or a mock treatment (gray columns) before data acquisition. The respective GFP fluorescence values are indicated by the Y axis and the standard errors are shown at the top of the columns. The numbers on top of some columns represent the fold of reporter induction of the induction treatment over the mock treatment.

FIG. 7. Compound screening using the direct fusion and the two-component transcriptional fusion systems. Cell lines transformed with prTARGET::GFP (the direct fusion reporter system) or prTARGET::LexA:Gal4_oplexA::GFP (the two-component reporter system) were used in a primary screen on a 30K diverse compound panel to identify compounds that can induce the prTARGET promoter, Fold of induction, calculated by the GFP florescence value of the test compound-treated group relative to that of the control (DMSO)-treated group, is represented on the X axis for two-component system, and on the Y axis for the direct fusion reporter system. Several compounds that did not meet the threshold of 2.5 fold induction with the direct fusion reporter line were identified as hits using the improved two-component system, demonstrating the improved sensitivity of the two-component system.

FIG. 8. Four (4) out of twenty (20) compound hits, identified from a primary screen using the two-component reporter line, “C71125”, “C66433”, “C71126” and “C71124”, conferred significant tolerance to desiccation stress with Arabidopsis seedlings relative to control compound, DMSO.

FIG. 9. A two-component transcriptional fusion system comprising a stress-inducible promoter RD29A. Cell lines transformed with prRD29A::LEXA:GAL4_opLEXA::GFP, i.e., “1-3-5”, “5-3-1”, “6-8-5”, “8-2-2”. “4-7-3”, “2-7-1”, and cell lines transformed with prRD29A::GFP (i.e., “RD29A”) or prRD29B::GFP, (i.e., “RD29B”), were subjected to an ABA induction (black columns), or a mock treatment (gray columns) before data acquisition. The relative GFP fluorescence values are indicated by the Y axis and the standard errors are shown at the top of the columns.

DETAILED DESCRIPTION

The instant description relates generally to reporter constructs and their use in gene regulation. The instant description provides methods for identification of chemical compounds that can be applied to enhance the performance or modify phenotypes of an organism or in vitro culture. Throughout this disclosure, various information sources are referred to and/or are specifically incorporated. The information sources include scientific journal articles, patent documents, textbooks, and World Wide Web browser-inactive page addresses. While the reference to these information sources clearly indicates that they can be used by one of skill in the art, each and every one of the information sources cited herein are specifically incorporated in their entirety, whether or not a specific mention of “incorporation by reference” is noted. The contents and teachings of each and every one of the information sources can be relied on and used to make and use embodiments of the instant description.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include the plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “a host cell” includes a plurality of such host cells, and a reference to “a stress” is a reference to one or more stresses and equivalents thereof known to those skilled in the art, and so forth.

DEFINITIONS

“Nucleic acid molecule” refers to an oligonucleotide, polynucleotide or any fragment thereof. It may be DNA or RNA of genomic or synthetic origin, double-stranded or single-stranded, and combined with carbohydrate, lipids, protein, or other materials to perform a particular activity such as transformation or form a useful composition such as a peptide nucleic acid (PNA).

“Polynucleotide” is a nucleic acid molecule comprising a plurality of polymerized nucleotides, e.g., at least about 15 consecutive polymerized nucleotides. A polynucleotide may be a nucleic acid, oligonucleotide, nucleotide, or any fragment thereof. In many instances, a polynucleotide comprises a nucleotide sequence encoding a polypeptide (or protein) or a domain or fragment thereof. Additionally, the polynucleotide may comprise a promoter, an intron, an enhancer region, a polyadenylation site, a translation initiation site, 5′ or 3′ untranslated regions, a reporter gene, a selectable marker, or the like. The polynucleotide can be single-stranded or double-stranded DNA or RNA. The polynucleotide optionally comprises modified bases or a modified backbone. The polynucleotide can be, e.g., genomic DNA or RNA, a transcript (such as an mRNA), a cDNA, a PCR product, a cloned DNA, a synthetic DNA or RNA, or the like. The polynucleotide can be combined with carbohydrate, lipids, protein, or other materials to perform a particular activity such as transformation or form a useful composition such as a peptide nucleic acid (PNA). The polynucleotide can comprise a sequence in either sense or antisense orientations. “Oligonucleotide” is substantially equivalent to the terms amplimer, primer, oligomer, element, target, and probe and is preferably single-stranded.

A “recombinant polynucleotide” is a polynucleotide that is not in its native state, e.g., the polynucleotide comprises a nucleotide sequence not found in nature, or the polynucleotide is in a context other than that in which it is naturally found, e.g., separated from nucleotide sequences with which it typically is in proximity in nature, or adjacent (or contiguous with) nucleotide sequences with which it typically is not in proximity. For example, the sequence at issue can be cloned into a vector, or otherwise recombined with one or more additional nucleic acid.

An “isolated polynucleotide” is a polynucleotide, whether naturally occurring or recombinant, that is present outside the cell in which it is typically found in nature, whether purified or not. Optionally, an isolated polynucleotide is subject to one or more enrichment or purification procedures, e.g., cell lysis, extraction, centrifugation, precipitation, or the like.

A “reporter polynucleotide” is a polynucleotide that encodes a reporter protein, whose expression level or activity can be quantified by colorimetric, fluorescent or luminescence signals. Commonly-used reporter proteins include but are not limited to, beta-galactosidase (LacZ), green fluorescent protein (GFP), luciferase (LUC), chloramphenicol transferase (CAT), and glucuronidase (GUS).

“Gene” or “gene sequence” refers to the partial or complete coding sequence of a gene, its complement, and its 5′ or 3′ untranslated regions. A gene is also a functional unit of inheritance, and in physical terms is a particular segment or sequence of nucleotides along a molecule of DNA (or RNA, in the case of RNA viruses) involved in producing a polypeptide chain. The latter may be subjected to subsequent processing such as chemical modification or folding to obtain a functional protein or polypeptide. A gene may be isolated, partially isolated, or found with an organism's genome. By way of example, a transcriptional regulatory polypeptide gene encodes a transcriptional regulatory polypeptide, which may be functional or require processing to function as an initiator of transcription.

Operationally, genes may be defined by the cis-trans test, a genetic test that determines whether two mutations occur in the same gene and that may be used to determine the limits of the genetically active unit (Rieger et al. (1976)^(i)). A gene generally includes regions preceding (“leaders”; upstream) and following (“trailers”; downstream) the coding region. A gene may also include intervening, non-coding sequences, referred to as “introns”, located between individual coding segments, referred to as “exons”. Most genes have an associated promoter region, a regulatory sequence 5′ of the transcription initiation codon (there are some genes that do not have an identifiable promoter). The function of a gene may also be regulated by enhancers, operators, and other regulatory elements.

A “transgenic or transformed plant” refers to a plant which contains a recombinant polynucleotide introduced by transformation. Transformation means introducing a nucleotide sequence in a plant in any manner to cause stable or transient expression of the sequence. This may be achieved by transfection with viral vectors, transformation with plasmids, such as Agrobacterium-based vectors, or introduction of naked DNA by electroporation, lipofection, or particle gun acceleration. A transformed plant may refer to a whole plant as well as to seed, plant tissue, plant cells or any other plant material, and to the plant's progeny.

A “transgenic organism” refers to an organism, such as a plant, a microbe, a mammal, yeast, Drosophila, C. elegans, etc., which contains a recombinant polynucleotide introduced by transformation. Transformation means introducing a nucleotide sequence in an organism in any manner to cause stable or transient expression of the sequence. This may be achieved by transfection with viral vectors, transformation with plasmids, or introduction of naked DNA by electroporation, lipofection, or particle gun acceleration. A transformed organism may refer to a whole organism, to any part of the organism, to any materials derived from the organism, and to an offspring of the organism.

A “vector” is a nucleic acid construct, generated recombinantly or synthetically, comprising nucleic acid elements that can cause expression of a gene. A “donor vector” is a construct for expression of a polynucleotide sequence for a transactivator gene. The transactivator gene is operably linked to a promoter. The promoter region may include tissue active-or-specific promoters, developmental stage active-or-specific promoters, inducible promoters or constitutive promoters.

A “polypeptide of interest” maybe any peptide, including, for example, a polypeptide sequence for a regulatory gene such as a transcriptional regulatory polypeptide, a protein kinase or a phosphatase. These sequences may be in a sense or antisense orientation, or partial or complete gene sequences.

The phrase “altered or modified expression” in reference to polynucleotide or polypeptide expression refers to an expression pattern in a transgenic organism that is different from the expression pattern in the wild type plant or a reference plant; for example, by expression in a cell type other than a cell type in which the sequence is expressed in the wild type plant, or by expression at a time other than at the time the sequence is expressed in the wild type plant, or by a response to different inducible agents, such as hormones or environmental signals, or at different expression levels (either higher or lower) compared with those found in a wild type plant. The term also refers to lowering the levels of expression to below the detection level or completely abolishing expression. The resulting expression pattern may be transient or stable, constitutive or inducible.

A “promoter” or “promoter region” refers to an RNA polymerase binding site on a segment of DNA, generally found upstream or 5′ relative to a coding sequence under the regulatory control of the promoter. The promoter will generally comprise response elements that are recognized by transcriptional regulatory polypeptides. transcriptional regulatory polypeptide may bind to the promoter sequences, recruiting RNA polymerase, which synthesizes RNA from the coding region. Dissimilarities in promoter sequences account for different efficiencies of transcription initiation and hence different relative expression levels of different genes.

“Promoter function” includes regulating expression of the coding sequences under a promoter's control by providing a recognition site for RNA polymerase and/or other factors, such as transcriptional regulatory polypeptides, all of which are necessary for the start of transcription at a transcription initiation site. A “promoter function” may also include the extent to which a gene coding sequence is transcribed to the extent determined by a promoter sequence.

The term “operably linked” refers to the association of polynucleotide sequences so that the function of one is affected by the other. For example, a promoter is operably linked with a coding sequence when it affects the expression of that coding sequence (i.e., that the coding sequence is under the transcriptional control of the promoter). Coding sequences can be operably linked to regulatory sequences in sense or antisense orientation. The polynucleotide molecules may be part of a single contiguous polynucleotide molecule and may be adjacent. For example, a promoter is operably linked to a gene of interest if the promoter modulates transcription of the gene of interest in a cell.

The term “DNA sequence-specific transactivator” refers to a polypeptide that comprises at least a DNA binding domain that binds to DNA with some degree of specificity and a transcriptional activation domain that has the function of activating transcription. A common feature of some activation domains is that they are designed to form amphiphilic alpha helices with negative charge (Giniger and Ptashne (1987) Nature 330:670-672, Gill and Ptashne (1987) Cell 51:121-126, Estruch et al (1994) Nucl. Acids Res. 22:3983-3989). Examples include the transcription activation region of VP16 or GAL4 (Moore et al. (1998) Proc. Natl. Acad. Sci. USA 95: 376-381; and Aoyama et al. (1995) Plant Cell 7:1773-1785), peptides derived from bacterial sequences (Ma and Ptashne (1987) Cell 51; 113-119) and synthetic peptides (Giniger and Ptashne, supra), or the EDLL domain from plants (Mendel's PCT application PCT/US2009/048814). Exemplary transactivators are those described in Brent and Ptashne, U.S. Pat. No. 4,833,080, herein incorporated by reference or in Hasselhoff and Hodge, WO97/30164.

“Activation” of a promoter-reporter construct is considered to be achieved when the activity value relative to control, e.g., a sample that is not treated with a test compound, is 105%, 110%, 120%, 130%, 140%, 150%, 200%, 250%, 300%, 400%, 500%, or 1000-3000% or more higher.

The phrases “coding sequence,” “structural sequence,” and “transcribable polynucleotide sequence” refer to a physical structure comprising an orderly arrangement of nucleic acids. The nucleic acids are arranged in a series of nucleic acid triplets that each form a codon. Each codon encodes for a specific amino acid. Thus the coding sequence, structural sequence, and transcribable polynucleotide sequence encode a series of amino acids forming a protein, polypeptide, or peptide sequence. The coding sequence, structural sequence, and transcribable polynucleotide sequence may be contained, without limitation, within a larger nucleic acid molecule, vector, etc. In addition, the orderly arrangement of nucleic acids in these sequences may be depicted, without limitation, in the form of a sequence listing, figure, table, electronic medium, etc.

A “polypeptide” is an amino acid sequence comprising a plurality of consecutive polymerized amino acid residues e.g., at least about 15 consecutive polymerized amino acid residues. In many instances, a polypeptide comprises a polymerized amino acid residue sequence that is a transcriptional regulatory polypeptide or a domain or portion or fragment thereof. Additionally, the polypeptide may comprise: (i) a localization domain; (ii) an activation domain; (iii) a repression domain; (iv) an oligomerization domain; (v) a protein-protein interaction domain; (vi) a DNA-binding domain; or the like. The polypeptide optionally comprises modified amino acid residues, naturally occurring amino acid residues not encoded by a codon, non-naturally occurring amino acid residues.

“Protein” refers to an amino acid sequence, oligopeptide, peptide, polypeptide or portions thereof whether naturally occurring or synthetic.

A “recombinant polypeptide” is a polypeptide produced by translation of a recombinant polynucleotide. A “synthetic polypeptide” is a polypeptide created by consecutive polymerization of isolated amino acid residues using methods well known in the art. An “isolated polypeptide,” whether a naturally occurring or a recombinant polypeptide, is more enriched in (or out of) a cell than the polypeptide in its natural state in a wild-type cell, e.g., more than about 5% enriched, more than about 10% enriched, or more than about 20%, or more than about 50%, or more, enriched, i.e., alternatively denoted: 105%, 110%, 120%, 150% or more, enriched relative to wild type standardized at 100%. Such an enrichment is not the result of a natural response of a wild-type organism. Alternatively, or additionally, the isolated polypeptide is separated from other cellular components with which it is typically associated, e.g., by any of the various protein purification methods herein.

The instant description also encompasses production of DNA sequences that encode polypeptides and derivatives, or fragments thereof, entirely by synthetic chemistry. After production, the synthetic sequence may be inserted into any of the many available expression vectors and cell systems using reagents well known in the art. Moreover, synthetic chemistry may be used to introduce mutations into a sequence encoding polypeptides or any fragment thereof.

“Derivative” refers to the chemical modification of a nucleic acid molecule or amino acid sequence. Chemical modifications can include replacement of hydrogen by an alkyl, acyl, or amino group or glycosylation, pegylation, or any similar process that retains or enhances biological activity or lifespan of the molecule or sequence.

The term “plant” includes whole plants, shoot vegetative organs/structures (for example, leaves, stems and tubers), roots, flowers and floral organs/structures (for example, bracts, sepals, petals, stamens, carpels, anthers and ovules), seed (including embryo, endosperm, and seed coat) and fruit (the mature ovary), plant tissue (for example, vascular tissue, ground tissue, and the like) and cells (for example, guard cells, egg cells, and the like), and progeny of same. The class of plants that can be used in the method of the instant description is generally as broad as the class of higher and lower plants amenable to transformation techniques, including angiosperms (monocotyledonous and dicotyledonous plants), gymnosperms, ferns, horsetails, psilophytes, lycophytes, bryophytes, and multicellular algae.

A “trait” refers to a physiological, morphological, biochemical, or physical characteristic of a plant or particular plant material or cell. In some instances, this characteristic is visible to the human eye, such as seed or plant size, or can be measured by biochemical techniques, such as detecting the protein, starch, or oil content of seed or leaves, or by observation of a metabolic or physiological process, e.g. by measuring tolerance to water deprivation or particular salt or sugar concentrations, or by the observation of the expression level of a gene or genes, e.g., by employing Northern analysis, RT-PCR, microarray gene expression assays, or reporter gene expression systems, or by agricultural observations such as hyperosmotic stress tolerance or yield. Any technique can be used to measure the amount of, comparative level of, or difference in any selected chemical compound or macromolecule in the transgenic plants, however.

“Trait modification” refers to a detectable difference in a characteristic in an organism being treated with the chemical compounds of the instant description relative to a control organism of the same species, the latter including organisms treated with a control compound or a carrier solvent or no treatment. In some cases, the trait modification can be evaluated quantitatively. For example, the trait modification can entail at least about a 2% increase or decrease, or an even greater difference, in an observed trait as compared with a control or wild-type organism. It is known that there can be a natural variation in the modified trait. Therefore, the trait modification observed entails a change of the normal distribution and magnitude of the trait in the plants as compared to control or wild-type organisms.

“Modulates” refers to a change in activity (biological, chemical, or immunological) or lifespan resulting from specific binding between a molecule and either a nucleic acid molecule or a protein.

“Ectopic expression or altered expression or modified expression” in reference to a polynucleotide indicates that the pattern of expression in, e.g., a transgenic organism or tissue, is different from the expression pattern in a wild-type organism or a reference organism of the same species. The pattern of expression may also be compared with a reference expression pattern in a wild-type plant of the same species. For example, the polynucleotide or polypeptide is expressed in a cell or tissue type other than a cell or tissue type in which the sequence is expressed in the wild-type organism, or by expression at a time other than at the time the sequence is expressed in the wild-type plant, or by a response to different inducible agents, such as hormones or environmental signals, or at different expression levels (either higher or lower) compared with those found in a wild-type organism. The term also refers to altered expression patterns that are produced by lowering the levels of expression to below the detection level or completely abolishing expression. The resulting expression pattern can be transient or stable, constitutive or inducible. In reference to a polypeptide, the term “ectopic expression or altered expression” further may relate to altered activity levels resulting from the interactions of the polypeptides with exogenous or endogenous modulators or from interactions with factors or as a result of the chemical modification of the polypeptides.

The term “overexpression” as used herein refers to a greater expression level of a gene in an organism, a cell or a tissue, compared to expression in a wild-type plant, cell or tissue, at any developmental or temporal stage for the gene. Overexpression can occur when, for example, the genes encoding one or more polypeptides are under the control of a strong promoter (e.g., the cauliflower mosaic virus 35S transcription initiation region). Overexpression may also occur under the control of an inducible or tissue specific promoter. Thus, overexpression may occur throughout an organism, in specific tissues of the organism, or in the presence or absence of particular environmental signals, depending on the promoter used.

Overexpression may take place in cells normally lacking expression of polypeptides functionally equivalent or identical to the present polypeptides. Overexpression may also occur in cells where endogenous expression of the present polypeptides or functionally equivalent molecules normally occurs, but such normal expression is at a lower level. Overexpression thus results in a greater than normal production, or “overproduction” of the polypeptide in the organism, cell or tissue.

The term “transcription regulating region” or “transcription regulating nucleic acid sequence” refers to a DNA regulatory sequence that regulates expression of one or more genes in an organism when a transcriptional regulatory polypeptide having one or more specific binding domains binds to the DNA regulatory sequence. Transcriptional regulatory polypeptides possess a conserved domain. The transcriptional regulatory polypeptides also comprise an amino acid subsequence that forms a transcription activation domain that regulates expression of one or more abiotic stress tolerance genes in an organism when the transcriptional regulatory polypeptide binds to the regulating region.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The instant description provides novel reporter gene constructs that could be used to study gene regulation and identify novel sequences and agents that can be used to modify a phenotype of interest. The reporter gene system of the instant description can be a transcriptional fusion reporter system or a translational fusion reporter system.

Transcriptional Fusion Reporter System

The transcriptional fusion reporter system of the instant description comprises a reporter gene that is regulated by: 1) a target promoter sequence recognized by a transcriptional regulatory polypeptide, and 2) a DNA sequence-specific transactivator.

The transcriptional fusion reporter system can be used to identify compounds that modulate the activity of a target promoter. Plants or plant cells transformed with the transcriptional fusion reporter constructs can be treated with test compounds or compound libraries, and reporter gene expression can be monitored. Alternatively, the transformed organisms or cells containing the transcriptional fusion reporter constructs can be placed in a panel of microtiter wells and a panel of test compounds can be added to the cells, one compound to each well. A useful compound can be identified based on its ability to generate an enhanced or decreased reporter signal relative to control compounds.

The target promoters suitable for use herein can be any promoter that is recognized and regulated by a transcriptional regulatory polypeptide, including those that are constitutively active or those that are inducible or tissue enhanced or developmental-stage active promoters. In a preferred embodiment, the target promoters are the ones that regulate plant trait development. The target promoters can be naturally derived or synthetically made. The minimal promoter for use in synthetic promoters can be from any promoter. The minimal promoter supports basal transcription and typically comprises regulatory elements such as TATAA sequences. Exemplary minimal promoter regions can be from promoters such as the cauliflower mosaic virus (CaMV) 35 S transcription initiation region, and other transcription initiation regions from various genes known to those of skill.

In some embodiments of the instant description, the target promoter activates the expression of a DNA sequence-specific transactivator, which recognizes and binds to a specific transcriptional regulatory sequence and induces high level reporter gene expression. For example, the target promoter could drive the expression of a translational fusion of a DNA binding domain (e.g., the LexA DNA binding domain) and a transcriptional activation domain (e.g., the Gal4 transcriptional activation domain). A reporter molecule would be expressed from a promoter bound by the DNA binding domain (e.g., the opLexA promoter) such that activation of the target promoter would result in amplified expression of the reporter gene mediated by the DNA sequence-specific transactivator (e.g., LEXA:GAL4) (FIG. 2). This system thus enables more sensitive reporter detection compared to direct promoter-reporter fusion construct, and is particularly advantageous when employing a promoter of a transcriptional regulatory polypeptide or for targets with low expression levels or when screening for compounds that can down-regulate the activity of a target promoter or a transcriptional regulatory polypeptide that recognizes the target promoter.

The DNA sequence-specific transactivator of the transcriptional fusion system can also comprise a dexamethasone responsive element, for example, a target promoter could drive the expression of a translational fusion of the LexA DNA binding domain, the Gal4 transcriptional activation domain and the ligand binding domain of the glucocorticoid receptor (GR). An example of this inducible reporter system involves introducing a dexamethasone-responsive cassette, e.g. a polynucleotide encoding a fusion protein LEXA:GAL4:GR, and a transcriptional fusion of a target promoter and a reporter gene into the cell, where the addition of dexamethasone results in high levels of expression of a transcriptional regulatory polypeptide, which would, in turn, activate a target promoter and result in high reporter expression (FIG. 1). These dexamethasone inducible reporter systems can be internally validated by the addition or withdrawal of dexamethasone and the expected reporter (e.g., the “reporter2” in FIG. 1) signal induction can be quantified prior to a high throughput screen. The benefit of this multi-component system would be the ease of identifying a candidate line with strong induction characteristics, eliminating lines with silencing or poor expression due to the chromosomal integration site. The control over the activation of the transgene by dexamethasone also minimizes the negative interference from constitutive expression of some transgenes. Furthermore, this dexamethasone-inducible system can achieve adjustable levels of reporter gene expression: in the absence of dexamethasone, endogenous transcriptional regulatory polypeptide binds to the target promoter and activates reporter gene expression to a relatively low level, while in the presence of dexamethasone, dexamethasone-inducible transactivator activates the expression of the exogenous transcriptional regulatory polypeptide, which in turn drives high level expression of the reporter gene; this system conveniently enables screening for chemistries that can repress (in the presence of dexamethansone) or activate (in the absence of dexamethasone) transcription from a target promoter with one singular construct and selected transgenic line;

A variant of the transcriptional fusion reporter system employs two different DNA sequence-specific transactivators with distinct DNA binding sequence specificities to activate reporter gene expression: a first DNA sequence-specific transactivator, in the presence of dexamethasone, induces the expression of a transcriptional regulatory polypeptide, which, in turn, binds its target promoter sequence and activates a second DNA sequence-specific transactivator, which subsequently activates the reporter gene expression (FIG. 3). A system as such assimilates advantages of both systems described above (and as shown in FIGS. 1 and 2) by incorporating an amplification component that boosts the sensitivity of the screen and a characterization component that eases the identification of suitable cell lines with strong induction characteristics.

In addition to compound screening, the transcriptional fusion reporter system can also be used to characterize novel promoter elements or promoter fragments in response to various environmental stimuli or activation signals. Any novel promoter element of interest can be used as a target promoter and incorporated in the transcriptional fusion reporter system, which is then introduced into the cells and monitored for the ability to affect reporter gene activity under conditions that can activate a control promoter. The promoter function of the novel target promoter elements can be evaluated based on the ability to activate or repress the reporter gene activity relative to the control promoter sequence under the same conditions.

Translational Fusion Reporter System

The translational fusion reporter system of the present description comprises at least 1) a polynucleotide encoding a DNA sequence specific transactivator, 2) a polynucleotide encoding a fusion protein, and 3) a nucleotide sequence recognized by the DNA sequence specific transactivator. The genetic elements of 1), 2) and 3) are arranged in a way such that the DNA sequence-specific transactivator activates the expression of a translational fusion of a reporter molecule and a polypeptide of interest.

The translational reporter system of the instant description can be used to identify compounds that can modulate the stability of a polypeptide of interest. Test compounds and control compounds are applied to the cells transformed with the translational fusion constructs. Test compounds that change the stability of polypeptides of interest can be identified based on the altered reporter gene activity levels relative to controls. Hit compounds can be applied to the organisms of interest, for example, plants, bacteria, cell cultures etc., and further validated for the ability to change the stability of the polypeptide of the interest using biochemical approaches that are known in the art.

The polypeptide of interest may be any polypeptide, but is preferably a regulatory polypeptide, such as a transcriptional regulatory polypeptide, a phosphatase or a protein kinase. The polypeptide of interest may be from any species, particularly plant species, in a naturally occurring form or from any source whether natural, synthetic, semi-synthetic or recombinant. The polypeptide sequences may also include fragments of the present amino acid sequences of a regulator polypeptide, in particular a fragment with biological activity. In one preferred embodiment, the polypeptides of interest are all the transcriptional regulatory polypeptides identified in a plant, such as those identified in Arabidopsis thaliana. These transcriptional regulatory polypeptides collectively control all gene expression in plants and thus control all plant traits.

The plant transcriptional regulatory polypeptides may belong to one of the following transcription factor families: the AP2 (APETALA2) domain transcription factor family (Riechmann and Meyerowitz (1998) J. Biol. Chem. 379:633-646); the MYB transcription factor family (Martin and Paz-Ares, (1997) Trends Genet. 13:67-73); the MADS domain transcription factor family (Riechmann and Meyerowitz (1997) J. Biol. Chem. 378:1079-1101); the WRKY protein family (Ishiguro and Nakamura (1994) Mol. Gen. Genet. 244:563-571); the ankyrin-repeat protein family (Zhang et al. (1992) Plant Cell 4:1575-1588); the zinc finger protein (Z) family (Klug and Schwabe (1995) FASEB J. 9: 597-604); the homeobox (HB) protein family (Duboule (1994) Guidebook to the Homeobox Genes, Oxford University Press); the CAAT-element binding proteins (Forsburg and Guarente (1989) Genes Dev. 3:1166-1178); the squamosa promoter binding proteins (SPB) (Klein et al. (1996) Mol. Gen. Genet. 1996 250:7-16); the NAM protein family (Souer et al. (1996) Cell 85:159-170); the IAA/AUX proteins (Rouse et al. (1998) Science 279:1371-1373); the HLH/MYC protein family (Littlewood et al. (1994) Prot. Profile 1:639-709); the DNA-binding protein (DBP) family (Tucker et al. (1994) EMBO J. 13:2994-3002); the bZIP family of transcription factors (Foster et al. (1994) FASEB J. 8:192-200); the Box P-binding protein (the BPF-1) family (da Costa e Silva et al. (1993) Plant J. 4:125-135); the high mobility group (HMG) family (Bustin and Reeves (1996) Prog. Nucl. Acids Res. Mol. Biol. 54:35-100); the scarecrow (SCR) family (Di Laurenzio et al. (1996) Cell 86:423-433); the GF14 family (Wu et al. (1997) Plant Physiol. 114:1421-1431); the polycomb (PCOMB) family (Kennison (1995) Annu. Rev. Genet. 29:289-303); the teosinte branched (TEO) family (Luo et al. (1996) Nature 383:794-799; the ABI3 family (Giraudat et al. (1992) Plant Cell 4:1251-1261); the triple helix (TH) family (Dehesh et al. (1990) Science 250:1397-1399); the EIL family (Chao et al. (1997) Cell 89:1133-44); the AT-HOOK family (Reeves and Nissen (1990)) Journal of Biological Chemistry 265:8573-8582); the S1FA family (Zhou et al. (1995) Nucleic Acids Res. 23:1165-1169); the bZIPT2 family (Lu and Ferl (1995) Plant Physiol. 109:723); the YABBY family (Bowman et al. (1999) Development 126:2387-96); the PAZ family (Bohmert et al. (1998) EMBO J. 17:170-80); a family of miscellaneous (MISC) transcription factors including the DPBF family (Kim et al. (1997) Plant J. 11:1237-1251) and the SPF1 family (Ishiguro and Nakamura (1994) Mol. Gen. Genet. 244:563-571); the golden (GLD) family (Hall et al. (1998) Plant Cell 10:925-936); or any other class of protein that is capable of directly or indirectly binding DNA and regulating the expression of a target gene.

Other transcriptional regulatory polypeptides may be identified by screening polynucleotide or polypeptide sequence databases, such as GenBank, using sequence alignment methods and homology calculations, such as those described in Altschul et al. (1994) Nature Genetics 6: 119-129. For example, the NCBI Basic Local Alignment Search Tool (BLAST) (Altschul et al. (1990) Basic local alignment search tool. J. Mol. Biol. 215:403-410) is available from several sources, including the National Center for Biotechnology Information (NCBI, Bethesda, Md., for use in connection with the sequence analysis programs blastp, blastn, blastx, tblastp, tblastn and tblastx). Alternatively, a program that identifies particular sequence motifs may be employed along with specific characteristic consensus sequences, such as FIND PATTERN (GCG, Madison, Wis.).

Exemplary plant transcriptional regulatory polypeptides that can be employed in the instant description include Gilmour et al. (1998) teach an Arabidopsis AP2 transcription factor, CBF1, which, when overexpressed in transgenic plants, increases plant freezing tolerance. For another example, Bruce et al. (2000); and Borevitz et al. (2000) teach that the PAP2 gene and other genes in the MYB family control anthocyanin biosynthesis through regulation of the expression of genes known to be involved in the anthocyanin biosynthetic pathway. Applicants' own patent publication no. US20080010703A1, which is herein incorporated by reference in its entirety, has disclosed regulatory proteins involved in plant light signaling pathways and alteration in the expression or activity of which have resulted in increased yield in plants. In addition, Applicants' patent publication no. US20090138981A1, which is herein incorporated by reference in its entirety, has listed transcriptional regulatory polypeptides that are involved in various plant signaling pathways and cellular events that impact on plant disease resistance, biomass production and abiotic stress tolerance. Accordingly, one skilled in the art would recognize that changing the expression of the present sequences in a plant would introduce modified traits not found in the wild-type cultivar or strain.

The DNA sequence-specific transactivator can be any transactivator that comprises at least a DNA binding domain and a transcriptional activation domain and has transcription-regulation activity, for example, a translational fusion of the LexA DNA binding domain and the Gal4 transcriptional activation domain. The translational fusion system of the instant description comprising DNA sequence-specific transactivator enables high level of reporter expression can be especially useful for identifying compounds that can decrease the stability of a polypeptide of interest (FIG. 4). Similar to what has been described in the transcriptional reporter system described above, various arrangements and combinations of sequences encoding DNA sequence-specific transactivator and dexamethasone inducible cassettes can be incorporated into the system in order to facilitate reporter line characterization and development, improve signal to noise ratio of the screening assay, and enhance screening efficiency. In addition, the various genetic elements included in both the transcriptional fusion reporter systems and translational fusion reporter systems described herein may reside in a single construct, or in multiple constructs with various selection markers. The multiple constructs can be transformed into an organism of interest, and transgenic organisms or cells carrying the desired genetic elements can be identified through the detection of the expression of appropriate selection markers. For example, a reporter system of the instant description may consist of two reporter constructs, with the polynucleotide encoding a DNA sequence-specific transactivator, e.g. LEXA:GAL4, comprised in one construct and the promoter responsive to the DNA sequence-specific transactivator, e.g. opLEXA, and the polynucleotide encoding the reporter or reporter fusion in the other.

Reporter Genes

Reporter genes suitable for use in the instant description are known to those of skill in the art. Reporters can be any protein, and include, but are not limited to, fluorescent proteins, such as green or red fluorescent proteins, or variants that produce a fluorescent color; β-glucuronidase (GUS); luciferase; chloramphenicol acetyltransferase; β-galactosidase; and alkaline phosphatase. Commonly used reporter genes include those encoding proteins that can generate quantifiable fluorescent, colorimetric, or luminescent signals. Transcription of the sequences encoding the reporter gene can be determined using any method known in the art. In some embodiments, protein activity of the reporter gene is measured, e.g., using a fluorescent reader or other instrumentation appropriate to the reporter system. Products to assist in determination of reporter activity are commercially available.

Samples that are treated with a test compound, or pool of test compounds, are compared to control samples without the test compound to examine the extent of modulation. Control samples (untreated with activators are assigned a relative activity value. Activation is then achieved when the reporter activity value relative to the control is 105%, 105-150%, optionally 150%, 150-500%, or 500-2000% or more, whereas down-regulation is achieved when the reporter activity value relative to the control is 70-90%, 66%, 20-50%, or 5-10%.

In other embodiments, endpoints other than reporter activity are assayed. For example, expression levels of the mRNA or protein can be measured to assess the effects of a test compound on reporter activation. In this instance, the expression of the reporter construct is measured by assessing the level of mRNA that encodes the reporter gene or the translational fusion of the reporter gene and a polypeptide of interest, or alternatively of the protein product. These assays can be performed using any methods known by those of skill in the art to be suitable. For example, mRNA expression can be detected using amplification-based methodologies, northern or dot blots, nuclease protection and the like. Polypeptide products can be identified using immunoassays.

Introduction of Reporter Constructs into Hosts or Host Cells

Reporter constructs can be introduced into the desired hosts or cells derived therefrom, such as plants, microbes, mammals, yeast, Drosophila, C. elegans by a variety of conventional and well-known techniques. For example, the vector can be introduced directly into the host cells using techniques such as electroporation, microinjection, and biolistic methods, such as particle bombardment.

Microinjection techniques are known in the art and well described in the scientific and patent literature. The introduction of DNA constructs using polyethylene glycol precipitation is described, e.g., in Paszkowski et al. (1984). Electroporation techniques are described in Fromm et al. (1985). Biolistic transformation techniques are described in Klein et al. (1987).

For transforming plants or plant cells, the reporter constructs may also be combined with suitable T-DNA flanking regions and introduced into a conventional Agrobacterium tumefaciens host vector. The virulence functions of the Agrobacterium tumefaciens host will direct the insertion of the construct and adjacent marker into the plant cell DNA when the cell is infected by the bacteria. Agrobacterium tumefaciens-mediated transformation techniques, including disarming and use of binary vectors, are well described in the scientific literature. See, for example Horsch et al. (1984), and Fraley et al. (1983).

The host plant cells for screening reporter constructs can be from any plant, including both dicots and monocots. Typically, plant cells are from Nicotiana benthamiana or Arabidopsis thaliana or another plant that is routinely transformed and assayed in the art.

Other plants also can be used in the screening methods taught herein. These include cereals, for example, maize, sorghum, rice, wheat, barley, oats, rye, milo, flax, or gramma grass. Other plant genera include, but are not limited to, Cucurbita, Rosa, Vitis, Juglans, Gragaria, Lotus, Medicago, Onobrychis; Trigonella, Vigna, Citrus, Linum, Geranium, Manihot, Daucus, Arabidopsis, Brassica, Raphanus, Sinapis, Atropa, Capsicum, Datura, Hyoscyamus, Lycopersicon, Nicotiana, Solanum, Petunia, Digitalis, Majorana, Ciahorium, Helianthus, Lactuca, Bromus, Asparagus, Antirrhinum, Heterocallis, Nemesis, Pelargonium, Panieum, Pennisetum, Ranunculus, Senecio, Salpiglossis, Cucumis, Browaalia, Glycine, Pisum, Phaseolus, Lolium, Oryza, Avena, Hordeum, Secale, Allium, and Triticum.

Following transformation of the reporter constructs into the plant cell, the transformed cell or plant tissue is selected or screened by conventional techniques. The transformed cell or plant tissue containing the reporter construct can then be regenerated, if desired, by known procedures. Additional methodology for the generation of plants comprising expression constructs for screening chemicals can be found in the art (see, e.g., U.S. Pat. No. 5,614,395).

Chemical Libraries

The compounds tested as modulators of yield regulators are typically chemical compounds. Essentially any chemical compound of interest can be used to activate or down-regulate the activity of the promoters of the instant description or to stabilize the polypeptides of the instant description using the assays as described. Most often, compounds can be dissolved in aqueous or organic (e.g., DMSO-based) solutions. The assays are designed to screen large chemical libraries and usually include automating the assay steps, which are typically run in parallel (e.g., in microtiter formats on microtiter plates in robotic assays). It will be appreciated that there are many suppliers of chemical compounds, including Sigma-Aldrich (St. Louis, Mo.), Fluka Chemika-Biochemica Analytika (Buchs, Switzerland) and the like.

In one preferred embodiment, high throughput screening methods involve providing a combinatorial chemical library containing a large number of test compounds. Such “combinatorial chemical libraries” are then screened in one or more assays, as described herein, to identify those library members (particular chemical species or subclasses) that activate or down-regulate the activity of the promoters of the instant description. The compounds thus identified serve as conventional “lead compounds” or can themselves be used as potential or actual agents for treating plants or other organisms.

A combinatorial chemical library is a collection of diverse chemical compounds generated by either chemical synthesis or biological synthesis, by combining a number of chemical “building blocks” such as reagents. For example, a linear combinatorial chemical library such as a polypeptide library is formed by combining a set of chemical building blocks (amino acids) in every possible way for a given compound length (i.e., the number of amino acids in a polypeptide compound). Millions of chemical compounds can be synthesized through such combinatorial mixing of chemical building blocks.

Preparation and screening of combinatorial chemical libraries is well known to those of skill in the art. Such combinatorial chemical libraries include, but are not limited to, small organic molecule libraries (see, e.g., U.S. Pat. No. 5,569,588; thiazolidinones and metathiazanones, U.S. Pat. No. 5,549,974; pyrrolidines, U.S. Pat. Nos. 5,525,735 and 5,519,134; morpholino compounds, U.S. Pat. No. 5,506,337; and the like). Other chemistries for generating chemical diversity libraries can also be used. Chemical diversity libraries are also commercially available, e.g., from such companies as 3-Dimensional Pharmaceuticals Inc., Albany Molecular Research Inc., Alchemia Pty. Ltd., Argonaut Technologies Inc., ArQuie Inc, Biofocus DPI, Array Biopharma Inc., Axys Pharmaceutical Inc., Cambridge Combinatorial Ltd., Charybdis Technologies Inc, ChemBridge Corp., CombiChem. Inc., ComGenex Inc., Discovery Partners International Inc., Diversa Corp., EnzyMed. Inc. Versicor, Gryphon Sciences Inc, Ixsys Inc., Kosan Biosciences Inc., Maxygen Inc., Molecumetics Ltd., Nanoscale Combinatorial Synthesis Inc., Ontogen Corp., Orchid Biocompter Inc., Oxford Asymmetry Ltd., Oxford Molecular Group PLC, Panlabs Inc., Pharmacopeia Inc., Phytera Inc., Proto Gene Inc., Sphere Biosystems Inc., Symyx Technologies Inc., and Systems Integration Drug Discovery Co.

Often, chemical libraries that are screened in the methods of the instant description comprise compounds with molecular weights between 150 and 600, an average c Log P value of 3 (range 0-9), an average number of R-bonding acceptors of 3.5 (range 0-9), an average number of R-bonding donors of one (range 0-4) and an average of three rotatable bonds (range 0-9). Such characteristics are typical of agrichemicals known in the art.

Devices for the preparation of combinatorial libraries are commercially available (see, e.g., 357 MPS, 390 MPS, Advanced Chem Tech, Louisville Ky., Symphony, Rainin, Woburn, Mass., 433A Applied Biosystems, Foster City, Calif., 9050 Plus, Millipore, Bedford, Mass.). In addition, numerous combinatorial libraries, are themselves commercially available (see, e.g., Chembridge, Inc., San Diego, Calif.; ComGenex, Princeton, N.J., Tripos, Inc., St. Louis, Mo., 3D Pharmaceuticals, Exton, Pa., Martek Biosciences, Columbia, Md., etc.).

High Throughput Assays

In the high throughput assays, it is possible to screen up to several thousand different test compounds in a single day. For example, each well of a microtiter plate can be used to run a separate assay against a selected test compound, or, if concentration or incubation time effects are to be observed, every 5-10 wells can test a single test compound. Further, pools of test compounds can also be tested where 25 multiple compounds are included in a single test sample. If a hit is then identified, the chemicals included in the pool can be individually tested to identify an active compound.

The compounds selected from the reporter assays are also evaluated using an additional screening step, for example, test compounds can be applied to an organism of interest and evaluated by measuring the presence or absence of a change in the level of the polypeptide of interest (if the compound is selected from the translational fusion reporter system) or a polypeptide that is regulated by the target promoter (if the compound is selected from the transcriptional fusion reporter system) by conventional methods known in the art, for example, RT-PCR analysis, western blot analysis, microarray hybridization, or sequencing based approaches.

In some embodiments of the instant description, the test compounds selected from the reporter gene system are subjected to a phenotypic analysis. A phenotypic analysis involves treating an organism with the test compound and detecting a modified trait which results from a change in the expression or activity of a polypeptide of interest, for example, a transcriptional regulatory polypeptide that regulates specific signaling pathways. In some embodiments, phenotypic analyses were performed on plants, which typically involve assays of abiotic stress tolerance, such as water deprivation, dehydration, or osmotic stress, or assays that measure photosynthetic capacity.

Treatment of Plants

Once chemical compounds are identified and further validated in accordance with the methods of the instant description, they can be used to treat any plant, for example, vegetable, fruit, and orchard crops, to enhance plant performance.

Plants that can be treated include both monocots and dicots and in particular, agriculturally important plant species, including but not limited to, crops such as soybean, wheat, corn, potato, cotton, rice, oilseed rape (including canola), sunflower, alfalfa, sugarcane and turf; or fruits and vegetables, such as banana, blackberry, blueberry, strawberry, and raspberry, cantaloupe, carrot, cauliflower, coffee, cucumber, eggplant, grapes, honeydew, lettuce, mango, melon, onion, papaya, peas, peppers, pineapple, spinach, squash, sweet corn, tobacco, tomato, watermelon, rosaceous fruits (such as apple, peach, pear, cherry and plum) and vegetable brassicas (such as broccoli, cabbage, cauliflower, Brussels sprouts and kohlrabi). Other crops, fruits and vegetables whose phenotype may be changed include barley, currant, avocado, citrus fruits such as oranges, lemons, grapefruit and tangerines, artichoke, cherries, nuts such as the walnut and peanut, endive, leek, roots, such as arrowroot, beet, cassaya, turnip, radish, yam, sweet potato and beans. Lower plants such as algae can also be treated in this manner.

The selected chemicals can be formulated for treating plants as a liquid or a solid form. For example, in liquid formulations, the plants can be treated with a spray, in a drench application, a drip application, or through irrigation. Formulations are prepared using known methodology and may comprise other reagents conventionally employed in formulation of agricultural chemicals, e.g., emulsifying agents, surfactants, etc. Examples of formulations include emulsifiable concentrates, directly sprayable or dilutable solutions, dilute emulsions, wettable powders, soluble powders, dusts, granules or microcapsules. The methods of application, such as spraying, atomizing, dusting, wetting, scattering or pouring, are selected in accordance with the desired application. For example, a slow-release formulation can be applied as a soil treatment so that a plant is exposed frequently to an isolated chemical (e.g., turf grass). In other instance, it may be desirable to incorporate a chemical compound selected in accordance with the method of the instant description into irrigation water for plants that experience frequent droughts (e.g., cotton).

EXAMPLES Example 1 Transcriptional Fusion Reporter System

The transcriptional fusion reporter system of the present invention comprises, in operable linkage, at least: a reporter gene, a target promoter sequence recognized by a transcriptional regulatory polypeptide, and a polynucleotide encoding a DNA sequence-specific transactivator. The reporter gene expression is controlled by the target promoter sequence and the DNA sequence-specific transactivator.

One exemplar transcriptional fusion reporter system expresses a dexamethasone-inducible transactivator, LEXA:GAL4:GR (SEQ ID NO: 1) and comprises: a) a transcriptional regulatory polypeptide encoded by a polynucleotide that is operably linked to the opLEXA promoter that is responsive to the dexamethasone-bound LEXA:GAL4:GR (SEQ ID NO: 2), and b) a reporter gene that is operably linked to the target promoter that is recognized by the transcriptional regulatory polypeptide. A DBD site::reporter1 component, for example, opLexA:reporter1, can also be included as a pre-characterization component to select cell lines and construct components that will impart strong inducible expression of the transcriptional regulatory polypeptide; under such circumstances, candidate polynucleotide sequence comprising promoter and DBD:AD:GR, and polynucleotide sequence of DBD site are introduced into a cell and their suitability for the screen are confirmed based on the ability of activating reporter expression (“reporter1”) in response to dexamethasone treatment (FIG. 1).

Another exemplar transcriptional fusion reporter system comprises: a) a polynucleotide encoding a DNA sequence-specific transactivator LEXA:GAL4 (SEQ ID NO: 4), which is operably linked to a target promoter that can be recognized by a plant transcriptional regulatory polypeptide; b) a reporter gene operably linked to a opLEXA promoter (SEQ ID NO: 5) (FIG. 2). FIG. 9 shows an example of such a system, where a RD29A promoter is employed to control the expression of a LEXA:GAL4 transactivator, which, in turn, activates the reporter gene expression through regulating the opLEXA promoter. This two component system has been shown to increase significantly the signal-to-noise ratio of the assay compared to the direct fusion system, where the target promoter controls the transcription of the reporter polynucleotide directly.

Another exemplar transcriptional fusion reporter system expresses a dexamethasone-inducible DNA sequence-specific transactivator, e.g., GAL4BD:VP16:GR (SEQ ID NO: 7). It also comprises: a) polynucleotide that encodes a transcriptional regulatory polypeptide, operably linked to the GAL4UAS promoter region (SEQ ID NO: 11) that is responsive to the dexamethasone-bound GAL4BD:VP16:GR (SEQ ID NO: 7); b) a LEXA:GAL4 polynucleotide (SEQ ID NO: 3) that is operably linked to a target promoter responsive to the transcriptional regulatory polypeptide; and c) a reporter gene that is operably linked to a opLEXA promoter (SEQ ID NO: 5) (FIG. 3). As described above, a DBD1 site::reporter1 component can also be included to select cell lines that can strongly induce the expression of the target transcriptional regulatory polypeptide using the DBD1site promoter element.

These reporter constructs from the transcriptional fusion reporter system can be introduced into plants or plant cells to screen for compounds that can be used to modulate the activity of a target promoter that is recognized by a transcriptional regulatory polypeptide. The reporter gene expression can be monitored and compounds are selected on the basis of their ability to alter reporter expression or activity relative to controls.

Example 2 Translational Fusion Reporter System

The translational fusion reporter system of the present description comprises at least: 1) a polynucleotide encoding a DNA sequence specific transactivator, 2) a polynucleotide encoding a fusion protein, and 3) a nucleotide sequence recognized by the DNA sequence specific transactivator. The genetic elements of 1), 2) and 3) are arranged in a way such that the expression of a translational fusion of a reporter molecule and a polypeptide of interest is activated by the DNA sequence-specific transactivator.

One exemplar translational fusion reporter system expresses a LEXA:GAL4 fusion (SEQ ID NO: 4) protein and comprises a polynucleotide encoding a translational fusion of a reporter molecule and a polypeptide of interest that is operably linked to a opLEXA promoter (SEQ ID NO: 5) that is responsive to the LEXA:GAL4 (FIG. 4).

The reporter constructs of the translational fusion reporter system can be introduced into plants or plant cells to screen for compounds that can modulate the stability of a polypeptide of interest. The reporter gene expression can be monitored and compounds are selected on the basis of their ability to alter reporter expression or activity relative to controls. Hit compounds can be applied to plants and further validated for the ability to change the stability of the polypeptide of the interest through biochemical analyses that are known in the art.

Example 3 The Two Component Transcription Fusion System has an Improved Signal-to-Noise Ratio Compared to a Direct Transcriptional Fusion

Aliquots of seeds for 10 independent lines harboring a prTARGET::LEXA:GAL4_opLEXA::GFP transgenic construct were surface sterilized (see Example 9), where prTARGET comprises a promoter element that regulates a gene involved in desiccation stress tolerance of Arabidopsis, and distributed into a 96-well polystyrene plate at a density of 5-10 seeds/well (n=16 wells) in standard liquid growth medium. In parallel, seeds were sterilized and distributed for the top performing prTARGET::GFP line previously identified from a study of over 20 independent lines based on the largest fold-increase in GFP reporter levels following an induction treatment which activates the promoter prTARGET. After six days of growth under 24 h hour light (100 microE m−2 s−1) at 25 degrees C., eight wells/line were given the “induction treatment” and the other eight were “mock treated” and the plate was returned to the growth chamber. After 48 additional hours the plate was removed and fluorescence levels acquired using a Synergy HT multimode reader in area scan mode. FIG. 6 shows the average fluorescence and the standard error of the mean. Several of the two-component lines out-performed the classic direct fusion using fold-induction and background fluorescence levels as the selection criteria.

Example 4 A Two-Component Transcriptional Fusion System Comprising a Stress-Inducible Promoter RD29A

Seeds from 10 independent lines harboring a prRD29A::LEXA:GAL4_opLEXA::GFP were surface-sterilized and plated in the same manner as described in Example 9 in parallel with the top-performing prRD29A::GFP and prRD29B::GFP line, which were identified previously from a study of multiple independent lines based on the largest fold-increase in GFP levels following an 1 μM ABA induction. Plants were grown in the same conditions as described in Example 3, except a 1 μM ABA induction which activates the RD29A and RD29B promoters was applied on day 5 of growth. Fluorescence levels of individual lines were acquired on day 8 and shown in FIG. 9. Several of the prRD29A::LEXA:GAL4_opLEXA::GFP exhibited significantly greater fold of GFP level increase upon ABA induction and less background fluorescence levels compared to the direct fusions, e.g. prRD29A::GFP and prRD29B::GFP lines.

Example 5 Compound Screen Using the Two Component System

Seeds from Arabidopsis lines transformed with prTARGET::GFP (direct fusion reporter system) or prTARGET::LexA:Gal4_oplexA::GFP (two component reporter system) described in Example 3 were used in a primary screen on a 30K diverse compound panel to identify compounds that can induce the prTARGET promoter using procedures described in Example 7. Compounds that showed at least 2.5 fold induction compared to DMSO were identified as “hits”. Several compounds that did not meet the threshold of 2.5 fold induction with the direct fusion reporter line (Y axis) were identified as hits using the improved two-component system (X axis), demonstrating the improved sensitivity of the two-component system (FIG. 7).

Twenty (20) compound hits, identified from the primary screen using the above-referenced prTARGET::LexA:Gal4_oplexA::GFP reporter line, were applied to wild type Arabidopsis seedlings according to Examples 9-10 in a secondary screen. Desiccation tolerance assays were performed according to the methods describe in Example 13 below. Four of these compounds, “C71125”, “C66433”, “C71126” and “C71124”, were confirmed to have conferred significant tolerance to desiccation stress to Arabidopsis seedlings relative to the control, DMSO (FIG. 8).

Example 6 Identifying Compounds that Modulate Signaling Pathways Relevant to Biotic Stress Tolerance, Abiotic Stress Tolerance, or Nitrogen Usage

Biotic stresses or abiotic stresses can induce changes in gene expression of signaling pathways that may potentiate a plant's natural defense against unfavorable conditions. A number of promoters have been selected from some of the marker genes involved in these pathways, i.e., genes that are up-regulated during the response of interest identified in the scientific literature or determined with in-house transcriptional profiling experiments. Promoters involved in signaling pathways of interest include but are not limited to drought-inducible promoters including sequences located in the promoter regions of At5g52310 (RD29A), At5g52300, AT1G16850, At3g46230, AT1G52690, At2g37870, AT5G43840, At5g66780, At3g17520, and At4g09600, disease inducible promoters including a regulatory sequence located in the promoter region of AT1G15125; and those that are inducible by a change of nitrogen status in the environment including sequences located in the promoter regions of AT1G13300, AT2G48080, AT3G25790, AT5G10210, and AT5G19970. The exemplary promoter sequences that can be used to identify compounds that can modulate plant's drought response, disease response, or nitrogen usage include SEQ ID NO: 29-44.

Any one of the aforementioned promoter sequences or their functional parts can be constructed into a two-component transcriptional fusion reporter system prGENE::LEXA:GAL4_opLEXA::GFP to screen for compounds that can induce the activity of prGENE and have beneficial effects on plant stress tolerance (prGENE represents any of the aforementioned promoters). A primary screen using said reporter system is performed by the method described in Example 7. Compounds that produce a greater than a pre-defined threshold level of induction of prGENE are identified as “hits” and applied to Arabidopsis wild-type seedlings according to the procedures in Example 9 and 10. Phenotypic assays (used as secondary screens) are performed according to the methods in Example 13. The compounds that yield the desired phenotypes in plants, such as increased stress tolerance, improved nitrogen use efficiency (NUE) and/or greater disease resistance, are then selected.

Example 7 Compound Screening

Sterile seeds are suspended in 0.5×MS, 0.5% sucrose, 0.05% MES and 0.1% Phytoblend agar at a density of 0.6 mg/mL and distributed to sterile 96-well polystyrene plates (250 μL/well). The plates are covered and sealed with breathable tape and incubated at 25° C. under 24-hour light (100 μE m−2 s−1) in a germination growth chamber. After six days, the plates are removed and treated with the test compounds or DMSO (1 μL, in duplicate plates), covered, sealed, and returned to the growth chamber for one more day. The plates are then removed, uncovered and queued for analysis. Green fluorescence protein (GFP, Ex 485 nm, Em 525 nm) is quantified on a TriStar Multimode Microplate Reader (Berthold, Rockville, Md.) in fluorescence area scan mode (3×3 grid, nine total scans/well). The average fluorescence for the nine scans is divided by the average fluorescence for all mock-treated wells (typically sixteen wells, 144 total scans) to obtain the per-plate activity ratio. The mean of the cross-plate duplicate activity ratios is then recorded. Additional statistical tests can be used to identify questionable sample data. A one-tailed heteroscedastic t-test was used between the treatment population (nine data points) and the control population (144 data points) and the Benjamini-Hochberg adjustment for multiple testing to generate a p(BH)-value was used for statistical significance. A high activity ratio and poor p(BH)-value (>0.05) is typically a result of a biased distribution of fluorescence within the test well. This can result from a seedling protruding towards the optical probe resulting in an erroneously high reading or punctate GFP expression from a dying seedling due to compound toxicity.

Example 8 Screening of a Chemical Library Using a Screening Assay in a High Throughput Format

A transcriptional fusion reporter construct or a translation fusion reporter construct of the instant description is transformed into plants. 1 μl each of the chemicals from a library purchased from a commercial source (such as ChemBridge™. Inc., San Diego, Calif.) is added to 96 well plates containing in each well 5-10 Arabidopsis seeds, which harbor a reporter construct encoding GFP, for instance of the type shown in FIGS. 1-4. The volume of the media in each well is 250 μl and the final concentration of the chemical in each well is 28 μM. The seeds are allowed to germinate and grow in the medium. The data are normalized based on negative controls in the same plate that are not treated with the chemical for one week and the GFP signal is quantified in a 96 well fluorescent reader (TriStar, Berthold, Oak Ridge, Tenn.).

An alternative screening method involves the germination and growth of the Arabidopsis seedlings harboring the GFP construct in 96 well plates for 4-7 days prior to the addition of the compound stock solutions. The seedlings are exposed to the compound solution for an additional 1-3 days and the GFP signal quantified in a 96 well fluorescent plate reader (TriStar, Berthold, Oak Ridge, Tenn.).

Example 9 Seed Preparation

Prior to plating, seeds for all experiments are surface sterilized in the following manner: (1) 5 minute incubation with mixing in 70% ethanol; (2) 20 minute incubation with mixing in 30% bleach, 0.01% Triton® X-100; (3) five rinses with sterile water. Seeds are resuspended in 0.1% sterile agarose and stratified at 4° C. for 2-4 days.

Example 10 Transplant Compound Treatment

Sterile stratified wild-type seeds (100 per plate) are sown on square plates containing the following medium: 80% MS solution, 1% sucrose, 0.05% MES, and 0.65% Phytoblend agar. Plates are incubated at 22° C. under 24-hour light (100 μE m−2 s−1) in a germination growth chamber. On day 8, the seedlings are transferred to 6-well assay plates at a density of 10 seedlings per well. The assay plates contained growth medium spiked with a unique test compound or DMSO (carrier solvent, 0.4% v/v) per well. The compound-treated seedlings are incubated at 22° C. under 24-hour light (100 μE m−2 s−1) in a germination growth chamber.

Example 11 Spray Compound Treatment Procedure

Sterile seeds (50 per plate) are sown on standard Petri dishes containing the following medium: 80% MS solution, 1% sucrose, 0.05% MES, and 0.65% Phytagar. Plates are incubated at 22° C. under 24-hour light (95 μE m−2 s−1) in a germination growth chamber. On day 8, the seedlings are transferred to square growth plates containing fresh medium (15-25 seedlings per plate) and arranged such that their primary roots are exposed and aligned in parallel along the surface of the plate. The plates are sealed with venting tape and returned to the growth chamber, oriented for vertical growth. Typically, on day 9, the plates are sprayed with a 0.01% Spreader Sticker surfactant solution containing the test compound or DMSO (carrier solvent, 0.4% v/v) using a Preval® aerosol sprayer (1.5 mL/plate). The plates are re-sealed and returned to the growth chamber (horizontal orientation). After an additional (assay-dependent) number of days in a growth chamber, the seedlings are then subjected to any of the plate-based abiotic or biotic stress resistance assays detailed below. Alternatively, the plants may be treated by spraying on soil either once or multiple times during growth using a formulated solution of the test compound (e.g. 0.01% Spreader Sticker); control plants are mock treated. The plants are then subjected to phenotypic validation analysis by means of morphological, developmental or abiotic/biotic stress resistance assays, such as in the example as described below.

Example 12 Genetic Marker Analysis

A compound identified in the screen analysis can also be evaluated for the effects on the genetic markers of a signaling pathway under physiological conditions where this signaling pathway is active. Such genetic marker assays are typically conducted after or concurrently with the primary screen measuring the activation or repression of the promoter-reporter construct, and can be performed using a variety of techniques known by those of skill in the art to be suitable. For example, mRNA expression can be detected using amplification-based methodologies, northern or dot blots, nuclease protection and the like. Polypeptide products can be identified using immunoassays. For example, to evaluate a compound for its effect on the genetic components (promoters or polypeptides) of the light signaling pathway, Arabidopsis seedlings are grown on solid media (50% MSIB5, 0.05% MES (PH 5.7), 0.5% sucrose, 0.8% agar) in a growth chamber at 22° C. with continuous light (95IlMollm2/s) for nine days. The seedlings are then transplanted onto media containing various chemicals (typically at 20 μM) or DMSO controls and returned to identical growth conditions for 6 h or 24 h. At the indicated time, the seedlings are removed from the media and immediately frozen in liquid nitrogen. RNA is extracted and cDNA is prepared using standard procedures known in the art. RT-PCR analysis is performed using primers for the genes that are critical component of the light signaling pathway, such as, for example, SEQ ID NOs: 2 and 28 of PCT publication WO2009/117448, the entire content of which is incorporated herein by reference.

Genetic marker activation or inhibition can also be determined by using reporter constructs. Such reporter constructs can, e.g., comprise the promoter sequences from the genetic markers, or alternatively, can comprise promoters form genes that are responsive to the genetic markers. Activation or inhibition using reporter constructs can be analyzed using the same methodology as that employed for evaluating the promoter-reporter activation/inhibition.

Example 13 Phenotypic Validation Analysis

In these Examples, unless otherwise indicated, morphological and physiological traits are disclosed for plants that are treated by a test compound in comparison to those treated by a control compound or a carrier solvent under the identical environmental conditions. Thus, a plant treated with a test compound that is described as large and/or drought tolerant is large and more tolerant to drought with respect to a control plant, the latter including plants treated with a control compound or a carrier solvent or no treatment. When a plant is said to have a better performance than controls, it generally is larger, have greater yield, and/or show less stress symptoms than control plants. The better performing lines may, for example, have produced less anthocyanin, or are larger, greener, more turgid, or more vigorous when challenged with a particular stress, compared to controls as noted below. Better performance generally implies greater size or yield, or tolerance to a particular biotic or abiotic stress, less sensitivity to ABA, or better recovery from a stress (as in the case of a soil-based drought treatment) than controls.

Phenotypic analyses can be performed according to what is known in the art, or with the following methods.

Morphological Analysis

Morphological analysis is performed to determine whether changes in transcriptional regulatory polypeptide levels or compound treatment affect plant growth and development. Arabidopsis seeds are cold-treated (stratified) on plates for three days in the dark (in order to increase germination efficiency) prior to transfer to growth cabinets. Initially, plates are incubated at 22° C. under a light intensity of approximately 100 microEinsteins for seven days. Seedlings (treated or untreated as described in Example 10 or 11) are then transferred onto soil (Sunshine® potting mix) Following transfer to soil, trays of seedlings are covered with plastic lids for 2-3 days to maintain humidity while they become established. Plants are grown on soil under fluorescent light at an intensity of 70-95 microEinsteins at a temperature of 18-23° C. and are optionally subjected to chemical treatments (or mock treatments) as described in Example 10 or 11. Light conditions consist of a 24-hour photoperiod unless otherwise stated. In instances where alterations in flowering time are apparent, flowering time may be re-examined under 8-hour, 12-hour and 24-hour light to assess whether the phenotype is photoperiod dependent. Under typical 24-hour light growth conditions, the typical generation time (seed to seed) for Arabidopsis is approximately 14 weeks.

Because many aspects of Arabidopsis development are dependent on localized environmental conditions, in all cases plants are evaluated in comparison to controls (i.e. plants that are untreated or treated with a control compound or a solvent carrier and are otherwise identical to the plants treated with the test compounds) in the same flat. Careful examination is made at the following stages: seedling (1 week), rosette (2-3 weeks), flowering (4-7 weeks), and late seed set (8-12 weeks). Seed is also inspected. Plants having no or few seeds are considered partially or totally sterile. Seedling morphology is assessed on selection plates. At all other stages, plants are macroscopically evaluated while growing on soil or another suitable growth medium. All significant differences (including alterations in growth rate, size, leaf and flower morphology, coloration and flowering time) are recorded, but routine measurements are not be taken if no differences are apparent. In certain cases, stem sections are stained to reveal lignin distribution. In these instances, hand-sectioned stems are mounted in phloroglucinol saturated 2M HCl (which stains lignin pink) and viewed immediately under a dissection microscope.

Physiological Analysis

Ten lines are typically examined in subsequent plate based physiology assays. A similar number of compound-treated plants are compared to controls when testing the effects of compound treatments.

Nitrogen Use Efficiency (NUE) Assay

There are multiple ways in which a plant can change nitrogen partitioning in response to changes in nitrogen availability. For example increased photosynthesis/seed dry weight or biomass. Routine measurements can be used to identify beneficial changes in nitrogen partitioning that result in plants with improved NUE.

One or multiple of the following parameters are assessed to determine the benefit to compound treated plants versus mock-treated control lines:

Photosynthesis: Light Saturated/Light Limited/Vcmax/Jmax/TPU limitation

Electron Transport: Light Saturated/Light limited

Respiration: Whole plant

Leaf chlorophyll content

Plant dry weight (root/shoot)

Plant carbon:nitrogen ratios (root/shoot)

Seed dry weight

Compound treatments that cause plant samples to deviate from controls in any of these relationships may improve nitrogen usage.

Plate Assays

Different plate-based physiological assays (shown below), representing a variety of abiotic and water-deprivation-stress related conditions, are used as a pre-screen to identify top performing lines (i.e. lines treated with a particular compound), that are generally then tested in subsequent soil based assays. Typically, ten lines are subjected to plate assays, from which the best three lines are selected for subsequent soil based assays.

In addition, a nutrient limitation assay can be used to find compounds that allow more plant growth upon deprivation of nitrogen. Nitrogen is a major nutrient affecting plant growth and development that ultimately impacts yield and stress tolerance. These assays monitor primarily root but also rosette growth on nitrogen deficient media. In all higher plants, inorganic nitrogen is first assimilated into glutamate, glutamine, aspartate and asparagine, the four amino acids used to transport assimilated nitrogen from sources (e.g. leaves) to sinks (e.g. developing seeds). This process may be regulated by light, as well as by C/N metabolic status of the plant. A C/N sensing assay is thus used to look for alterations in the mechanisms plants use to sense internal levels of carbon and nitrogen metabolites which could activate signal transduction cascades that regulate the transcription of N-assimilatory genes. To determine whether these mechanisms are altered or modified, we exploit the observation that control plants grown on media containing high levels of sucrose (3%) without a nitrogen source accumulate high levels of anthocyanins. This sucrose-induced anthocyanin accumulation can be relieved by the addition of either inorganic or organic nitrogen. Glutamine is used as a nitrogen source since it also serves as a compound used to transport N in plants.

Growth Assays

Unless otherwise stated, experiments are typically performed with the Arabidopsis thaliana ecotype Columbia (col-0), soybean or maize plants.

Growth assays may be conducted with Arabidopsis or other plant species (e.g., soy, maize, etc.) that are treated or untreated with test compounds or control as described in Examples 10 or 11. For example, Arabidopsis seedlings are grown on solid media (50% MS/B5, 0.05% MES (pH 5.7), 0.5% sucrose, 0.8% agar) in a growth chamber at 22° C. with continuous light (95 μMol/m2/s) for nine days. The seedlings are then transplanted onto media containing various chemicals (typically at 20 μM) or DMSO controls and returned to identical growth conditions for three additional days. Growth assays may assess tolerance to severe desiccation (a type of water deprivation assay), growth in cold conditions at 8° C., root development (visual assessment of lateral and primary roots, root hairs and overall growth), and phosphate limitation.

For the nitrogen limitation assay, plants are grown in 80% Murashige and Skoog (MS) medium in which the nitrogen source is reduced to 20 mg/L of NH₄NO₃. Note that 80% MS normally has 1.32 g/L NH₄NO₃ and 1.52 g/L KNO₃.

For phosphate limitation assays, seven day old seedlings are germinated on phosphate-free MS medium in which KH₂PO₄ is replaced by K₂SO₄.

For chilling growth assays, seeds are germinated and grown for seven days on MS+Vitamins+1% sucrose at 22° C. and are then transferred to chilling conditions at 8° C. and evaluated after another 10 days and 17 days.

For desiccation (plate-based water deprivation) assays, sterile, stratified wild-type seeds (100 per plate) were sown on square plates and on day 8 the seedlings were subjected to treatment by a unique test compound or a control compound according to Example 10 or 11. On day 11 the assay plates were photographed and placed in a laminar flow hood with the lid removed for 3 hours, rotating the plates 180 degrees after 90 minutes. The seedlings were then removed from the medium, placed on the surface of the inverted lid and desiccated an additional 3.6 hours. The seedlings were then transferred to square plates containing fresh growth medium, returned to the growth chamber and allowed to recover for 3-4 days prior to photo documentation and scoring.

For the polyethylene glycol (PEG) hyperosmotic stress tolerance screen, plant seeds are gas sterilized with chlorine gas for 2 h. The seeds are plated on each plate containing 3% PEG, ½×MS salts, 1% phytagel, and 10 μg/ml glufosinate-ammonium (BASTA). Two replicate plates per seed line are planted. The plates are placed at 4° C. for three days to stratify seeds. The plates are held vertically for 11 additional days at temperatures of 22° C. (day) and 20° C. (night). The photoperiod is 16 h. with an average light intensity of about 120 μmol/m2/s. The racks holding the plates are rotated daily within the shelves of the growth chamber carts. At 11 days, root length measurements are made. At 14 days, seedling status is determined, root length is measured, growth stage is recorded, the visual color is assessed, pooled seedling fresh weight is measured, and a whole plate photograph is taken.

Germination assays may also be carried out with NaCl (150 mM, to measure tolerance to salt), sucrose (9.4%, to measure altered or modified sugar sensing), cold (8° C.) or heat (32° C.). All germination assays are performed in aseptic conditions. Growing the plants under controlled temperature and humidity on sterile medium produces uniform plant material that has not been exposed to additional stresses (such as water stress) which could cause variability in the results obtained.

Prior to plating, seed for all experiments are surface sterilized in the following manner: (1)₅ minute incubation with mixing in 70% ethanol, (2) 20 minute incubation with mixing in 30% bleach, 0.01% triton-X 100, (3) 5× rinses with sterile water, (4) Seeds are re-suspended in 0.1% sterile agarose and stratified at 4° C. for 3-4 days. All germination assays follow modifications of the same basic protocol. Sterile seeds may be sown on conditional media that has a basal composition of 80% MS+Vitamins, or media containing test compounds as described in Example 6 above. Plates may be incubated at 22° C. under 24-hour light (120-130 μE m−2 s−1) in a growth chamber. Evaluation of germination and seedling vigor may be performed five days after planting.

Chlorophyll content, an indicator of photosynthetic capacity, may be measured with a SPAD meter.

Wilt Screen Assay

Soybean plants treated with test compounds or DMSO are grown in 5″ pots in growth chambers. After the seedlings reach the V1 stage (the V1 stage occurs when the plants have one trifoliolate, and the unifoliolate and first trifoliolate leaves are unrolled), water is withheld and the drought treatment thus started. A drought injury phenotype score is recorded, in increasing severity of effect, as 1 to 4, with 1 designated no obvious effect and 4 indicating a dead plant. Drought scoring is initiated as soon as one plant in one growth chamber had a drought score of 1.5. Scoring continues every day until at least 90% of the wild type plants achieve scores of 3.5 or more. At the end of the experiment the scores for both test compound treated and control soybean seedlings are statistically analyzed using Risk Score and Survival analysis methods (Glantz (2001); Hosmer and Lemeshow (1999).

Water Use Efficiency (WUE) Assay

WUE is estimated by exploiting the observation that elements can exist in both stable and unstable (radioactive) forms. Most elements of biological interest (including C, H, O, N, and S) have two or more stable isotopes, with the lightest of these being present in much greater abundance than 14_(C)=the others. For example, ¹²C is more abundant than ¹³C in nature (¹²C 98.89%, ¹³C=1.11%, <10-10%). Because ¹³C is slightly larger than ¹²C, fractionation of CO₂ during photosynthesis occurs at two steps:

1. ¹²CO₂ diffuses through air and into the leaf more easily;

2. ¹²CO₂ is preferred by the enzyme in the first step of photosynthesis, ribulose bisphosphate carboxylase/oxygenase.

WUE has been shown to be negatively correlated with carbon isotope discrimination during photosynthesis in several C3 crop species. Carbon isotope discrimination has also been linked to drought tolerance and yield stability in drought-prone environments and has been successfully used to identify genotypes with better drought tolerance. ¹³C/¹²C content is measured after combustion of plant material and conversion to CO₂, and analysis by mass spectroscopy. With comparison to a known standard, ¹³C content is altered in such a way as to suggest that treatment with test compounds improves water use efficiency.

Another potential indicator of WUE is stomatal conductance, that is, the extent to which stomata are open.

Data Interpretation

At the time of evaluation, plants are typically given one of the following qualitative scores:

-   -   (++) Substantially enhanced performance compared to controls.         The phenotype is very consistent and growth is significantly         above the normal levels of variability observed for that assay.     -   (+) Enhanced performance compared to controls. The response is         consistent but is only moderately above the normal levels of         variability observed for that assay.     -   (wt) No detectable difference from wild-type controls.     -   (−) Impaired performance compared to controls. The response is         consistent but is only moderately above the normal levels of         variability observed for that assay.     -   (−−) Substantially impaired performance compared to controls.         The phenotype is consistent and growth is significantly above         the normal levels of variability observed for that assay.

(n/d) Experiment failed, data not obtained, or assay not performed.

Soil Drought (Clay Pot)

The soil drought assay (typically performed on Arabidopsis in clay pots) is based on that described by Haake et al. (2002).

Sterile seeds (50 per plate) are sown on standard Petri dishes containing the following medium: 80% MS solution, 1% sucrose, 0.05% MES, and 0.65% Phytagar. Plates are incubated at 22° C. under 24-hour light (95 μE m−2 s−1) in a germination growth chamber. After seven days of growth the seedlings are transplanted to 3.5 inch diameter clay pots containing 80g of a 50:50 mix of vermiculite:perlite topped with 80 g of ProMix. Typically, each pot contains 14 evenly spaced seedlings. The pots are maintained in a growth room under 24-hour light conditions (18-23° C., and 90-100 μE m−2 s−1) and watered for a period of 14 days. Compounds (or DMSO) are applied as a 0.01% Spreader Sticker solution (or similar formulation) using a Preval aerosol sprayer (ca. 2 mL/pot or 100 g/ha) no more than three times during days 7-13 post-transplant. Water is then withheld and pots are placed on absorbent diaper paper for a period of 8-10 days to apply a drought treatment. At the end of the drought period, pots are re-watered and then scored after 5-6 additional days. The number of surviving plants in each pot is counted, and the survival percentage calculated.

In a given experiment, six or more pots of plants treated by test compounds with six or more pots of the appropriate control are typically compared. The mean drought score and mean proportion of plants surviving (survival rate) are calculated for both the transgenic line and the wild-type pots. In each case a p-value* is calculated, which indicates the significance of the difference between the two mean values.

For the assays where control and experimental plants are in separate pots, survival is analyzed with a logistic regression to account for the fact that the random variable is a proportion between 0 and 1. The reported p-value is the significance of the experimental proportion contrasted to the control, based upon regressing the logit-transformed data.

Drought score, being an ordered factor with no real numeric meaning, is analyzed with a non-parametric test between the experimental and control groups. The p-value is calculated with a Mann-Whitney rank-sum test.

Disease Resistance

Resistance to pathogens, such as Sclerotinia sclerotiorum and Botrytis cinerea, can be assessed in plate-based assays. Unless otherwise stated, all experiments are performed with the Arabidopsis thaliana ecotype Columbia (Col-0). Control plants for assays on lines containing direct promoter-fusion constructs are wild-type plants or Col-0 plants transformed an empty transformation vector (pMEN65).

Prior to plating, seed for all experiments are surface sterilized in the following manner: (1) 5 minute incubation with mixing in 70% ethanol; (2) 20 minute incubation with mixing in 30% bleach, 0.01% Triton X-100™; (3) five rinses with sterile water. Seeds are resuspended in 0.1% sterile agarose and stratified at 4° C. for 2-4 days.

Sterile seeds are sown on starter plates (15 mm deep) containing 50% MS solution, 1% sucrose, 0.05% MES, and 1% Bacto™-Agar. 40 to 50 seeds are sown on each plate. Seedlings are grown on solid media (50% MS/B5, 0.05% MES (pH 5.7),0.5% sucrose, 0.8% agar) in a growth chamber at 22° C. with continuous light (95 μMol/m2/s) for nine days. The seedlings are then transplanted onto media containing various chemicals (typically at 20 μM) or DMSO controls and returned to identical growth conditions for three additional days. Seedlings are then transferred to assay plates (25 mm deep plates with medium minus sucrose). On day 14, seedlings are inoculated (specific method below). After inoculation, plates are put in a growth chamber under a 12-hour light/12-hour dark schedule. Light intensity is lowered to 70-80 μE m−2 s−1 for the disease assay.

Sclerotinia inoculum preparation. A Sclerotinia liquid culture is started three days prior to plant inoculation by cutting a small agar plug (¼ sq. inch) from a 14- to 21-day old Sclerotinia plate (on Potato Dextrose Agar; PDA) and placing it into 100 ml of half-strength Potato Dextrose Broth. The culture is allowed to grown in the Potato Dextrose Broth at room temperature under 24-hour light for three days. On the day of seedling inoculation, the hyphal ball is retrieved from the medium, weighed, and ground in a blender with water (50 ml/gm tissue). After grinding, the mycelial suspension is filtered through two layers of cheesecloth and the resulting suspension is diluted 1:5 in water. Plants are inoculated by spraying to run-off with the mycelial suspension using a Preval aerosol sprayer.

Botrytis inoculum preparation. Botrytis inoculum is prepared on the day of inoculation. Spores from a 14- to 21-day old plate (on PDA) are resuspended in a solution of 0.05% glucose, 0.03M KH₂PO₄ to a final concentration of 10⁴ spores/ml. Seedlings are inoculated with a Preval aerosol sprayer, as with Sclerotinia inoculation.

Resistance to Erysiphe cichoracearum is assessed in a soil-based assay. Erysiphe cichoracearum is propagated on a pad4 mutant line in the Col-0 background, which is highly susceptible to Erysiphe (Reuber et al. (1998), or on squash plants, since this particular species of Erysiphe also parasitizes squash. Inocula are maintained by using a small paintbrush to dust conidia from a 2-3 week old culture onto 4-week old plants. For the assay, seedlings are grown on plates for one week under 24-hour light in a germination chamber, then transplanted to soil and grown in a walk-in growth chamber under a 12-hour light/12-hour dark light regimen, 70% humidity. Each line is transplanted to two 13 cm square pots, nine plants per pot. In addition, three control plants are transplanted to each pot, for direct comparison with the test line. Approximately 3.5 weeks after transplanting, plants are inoculated using settling towers, as described by Reuber et al., 1998. Generally, three to four heavily infested leaves are used per pot for the disease assay. Level of fungal growth is evaluated eight to ten days after inoculation.

It is expected that the same methods may be applied to identify other useful and valuable promoter sequences, and the sequences may be derived from a diverse range of species.

Embodiments of the Instant Description Embodiment 1

One or more reporter gene constructs comprising (a) a target promoter sequence that is capable of being recognized by a transcription factor, (b) a polynucleotide sequence that encodes a DNA sequence-specific transactivator, and (c) a reporter polynucleotide,

wherein the target promoter sequence and the DNA sequence-specific transactivator cooperatively regulate expression of the reporter polynucleotide.

Embodiment 2

The one or more reporter gene constructs of Embodiment 1, wherein the sequence specific transactivator is capable of binding a regulatory region of the reporter polynucleotide.

Embodiment 3

The one or more reporter gene constructs of Embodiment 1, wherein the sequence specific transactivator is capable of binding a regulatory region of a polynucleotide that encodes the transcription factor.

Embodiment 4

The one or more reporter gene constructs of Embodiment 1, wherein the transcription factor is capable of binding a regulatory region of the reporter polynucleotide.

Embodiment 5

The one or more reporter gene constructs of Embodiment 1, wherein the DNA sequence-specific transactivator is DBD:AD;

wherein AD comprised at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26; and

wherein DBD comprised at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18.

Embodiment 6

The one or more reporter gene constructs of Embodiment 1, wherein the DNA sequence-specific transactivator is a steroid-inducible transactivator, which regulates transcription of the transcription factor when bound by a steroid.

Embodiment 7

The one or more reporter gene constructs of Embodiment 6, wherein the steroid-inducible transactivator is DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 16 and 18;

wherein GR comprises SEQ ID NO: 14; and

wherein the steroid is dexamethasone.

Embodiment 8

The one or more reporter gene constructs of Embodiment 6, wherein the one or more reporter gene constructs further comprise a polynucleotide sequence that encodes an additional DNA sequence-specific transactivator,

wherein the additional DNA sequence-specific transactivator regulates transcription of the reporter gene through binding of its cognate sequence that is operably linked to the reporter polynucleotide.

Embodiment 9

The one or more reporter gene constructs of Embodiment 8, wherein the transcription factor is capable of binding a regulatory region of a polynucleotide encoding the additional DNA sequence-specific transactivator.

Embodiment 10

The one or more reporter gene constructs of Embodiment 8, wherein the steroid-inducible transactivator is DBD:AD:GR;

wherein AD is selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD is selected form the group consisting of SEQ ID NOs: 16 and 18;

wherein GR comprises SEQ ID NO: 14; and

wherein the steroid is dexamethasone.

Embodiment 11

One or more reporter gene constructs comprising a polynucleotide encoding a DNA sequence-specific transactivator and a polynucleotide encoding a translational fusion of a reporter gene molecule and a polypeptide of interest,

wherein the DNA sequence-specific transactivator regulates expression of the translational fusion.

Embodiment 12

The one or more reporter gene constructs of Embodiment 11, wherein the DNA sequence-specific transactivator is DBD:AD:GR;

wherein AD is selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD is selected form the group consisting of SEQ ID NOs: 16 and 18; and

wherein GR comprises SEQ ID NO: 14.

Embodiment 13

A transgenic cell comprising (a) a target promoter sequence that is capable of being recognized by a transcription factor, (b) a polynucleotide sequence that encodes a DNA sequence-specific transactivator, and (c) a reporter polynucleotide,

wherein the target promoter and the DNA sequence-specific transactivator cooperatively regulates expression of the reporter gene.

Embodiment 14

The transgenic cell of Embodiment 13, wherein the sequence specific transactivator is capable of binding a regulatory region of the reporter polynucleotide.

Embodiment 15

The transgenic cell of Embodiment 13, wherein the sequence specific transactivator is capable of binding a regulatory region of a polynucleotide that encodes the transcription factor.

Embodiment 16

The transgenic cell of Embodiment 13, wherein the transcription factor is capable of binding a regulatory region of the reporter polynucleotide.

Embodiment 17

The transgenic cell of Embodiment 13, wherein the DNA sequence-specific transactivator is DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18; and

wherein GR comprises SEQ ID NO: 14.

Embodiment 18

The transgenic cell of Embodiment 13, wherein the DNA sequence-specific transactivator is a steroid-inducible transactivator, which regulates transcription of the transcription factor when bound by a steroid.

Embodiment 19

The transgenic cell of Embodiment 18, wherein the steroid-inducible transactivator is

DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18;

wherein GR comprises SEQ ID NO: 14; and

wherein the steroid is dexamethasone.

Embodiment 20

The transgenic cell of Embodiment 18, further comprises a polynucleotide sequence that encodes an additional DNA sequence-specific transactivator and is located at 3′ relative to the steroid-inducible transactivator and 5′ relative to the reporter gene,

wherein the additional DNA-sequence-specific transactivator regulates transcription of the reporter gene through binding of its cognate sequence that is operably linked to the reporter polynucleotide.

Embodiment 21

The transgenic cell of Embodiment 19, wherein the transcription factor is capable of binding a regulatory region of a polynucleotide encoding the additional DNA sequence-specific transactivator.

Embodiment 22

The transgenic cell of Embodiment 19, wherein the steroid-inducible transactivator is

DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18;

wherein GR comprises SEQ ID NO: 14; and

wherein the steroid is dexamethasone.

Embodiment 23

A transgenic cell comprising a polynucleotide encoding a DNA sequence-specific transactivator and a polynucleotide encoding a translational fusion of a reporter gene molecule and a polypeptide of interest,

wherein the DNA sequence-specific transactivator regulates expression of the translational fusion.

Embodiment 24

The transgenic cell of Embodiment 23, wherein the DNA sequence-specific transactivator is DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 16 and 18; and

wherein GR comprises SEQ ID NO: 14.

Embodiment 25

The transgenic cell of Embodiment 13, wherein the transgenic cell is a cell derived from plants, mammals, microbes, Drosophila, Caenorhabditis, or yeast.

Embodiment 26

A method of screening for useful compounds comprising the steps of:

-   -   (a) contacting at least one test compound with a transgenic cell         comprising a target promoter sequence that is capable of being         recognized by a transcription factor, a polynucleotide sequence         that encodes a DNA sequence-specific transactivator, and a         reporter polynucleotide,         -   wherein the target promoter and the DNA sequence-specific             transactivator cooperatively regulate expression of the             reporter gene; and     -   (b) selecting a compound that alters the reporter gene activity         relative to controls.

Embodiment 27

The method of Embodiment 26, wherein the sequence specific transactivator is capable of binding a regulatory region of the reporter polynucleotide.

Embodiment 28

The method of Embodiment 26, wherein the sequence specific transactivator is capable of binding a regulatory region of a polynucleotide that encodes the transcription factor.

Embodiment 29

The method of Embodiment 26, wherein the transcription factor is capable of binding a regulatory region of the reporter polynucleotide.

Embodiment 30

The method of Embodiment 26, wherein the DNA sequence-specific transactivator is

DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18; and

wherein GR comprises SEQ ID NO: 14.

Embodiment 31

The method of Embodiment 26, wherein the DNA sequence-specific transactivator is a steroid-inducible transactivator, which regulates transcription of the transcription factor when bound by a steroid.

Embodiment 32

The method of Embodiment 31, wherein the steroid-inducible transactivator is

DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18;

wherein GR comprises SEQ ID NO: 14; and

wherein the steroid is dexamethasone.

Embodiment 33

The method of Embodiment 31, wherein the transgenic cell further comprises a polynucleotide sequence that encodes an additional DNA sequence-specific transactivator,

wherein the additional DNA-sequence-specific transactivator regulates transcription of the reporter gene through binding of its cognate sequence that is operably linked to the reporter polynucleotide.

Embodiment 34

The method of Embodiment 33, wherein the transcription factor is capable of binding a regulatory region of a polynucleotide encoding the additional DNA sequence-specific transactivator.

Embodiment 35

The method of Embodiment 33, wherein the dexamethasone steroid-inducible transactivator is

DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18;

wherein GR comprises SEQ ID NO: 14; and

wherein the steroid is dexamethasone.

Embodiment 36

A method of screening for useful compounds comprising the steps of:

(a) contacting at least one test compound with a transgenic cell comprising a polynucleotide encoding a DNA sequence-specific transactivator and a polynucleotide encoding a translational fusion of a reporter gene molecule and a polypeptide of interest,

-   -   wherein the DNA sequence-specific transactivator regulates         expression of the translational fusion; and

(b) selecting a compound that alters the reporter gene activity relative to controls.

Embodiment 37

The method of Embodiment 36, wherein the DNA sequence-specific transactivator is

DBD:AD:GR;

wherein AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26;

wherein DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and 18; and

wherein GR comprises SEQ ID NO: 14.

Embodiment 38

The method of Embodiment 26 further comprising the step of:

-   -   (c) contacting a plant with the selected compound and detecting         a modified trait in the plant relative to controls.

Embodiment 39

The method of Embodiment 36 further comprising the step of:

-   -   (c) contacting a plant with the selected compound and detecting         a modified trait in the plant relative to controls.

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All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The present description is not limited by the specific embodiments described herein. The instant description now being fully described, it will be apparent to one of ordinary skill in the art that many changes and modifications can be made thereto without departing from the spirit or scope of the appended claims. Modifications that become apparent from the foregoing description and accompanying figures fall within the scope of the claims. 

What is claimed is:
 1. A method of screening for useful compounds comprising the steps of: (a) contacting at least one test compound with a transgenic cell comprising a target promoter sequence that is operably linked to a polynucleotide sequence that encodes a DNA sequence-specific transactivator, and a reporter polynucleotide that is operably linked to a promoter sequence that can be recognized by the DNA sequence-specific transactivator; and (b) selecting a compound that alters the reporter gene activity relative to controls.
 2. The method of claim 1, wherein the DNA sequence-specific transactivator is a translational fusion of a DNA binding domain (DBD) and a transcriptional activation domain (AD); wherein the AD comprises at least one sequence selected from the group consisting of SEQ ID NOs: 20, and 22-26; and wherein the DBD comprises at least one sequence selected form the group consisting of SEQ ID NOs: 16 and
 18. 3. The method of claim 1, wherein the reporter polynucleotide encodes a polypeptide that is selected from the group of green fluorescent protein, luciferase, chloramphenicol transferase, and glucuronidase.
 4. The method of claim 1, wherein the target promoter sequence is selected from the group consisting of an AT5G52310 (RD29A) promoter, an At5g52300 promoter, an AT1G16850 promoter, an At3g46230 promoter, an AT1G52690 promoter, an At2g37870 promoter, an AT5G43840 promoter, an At5g66780 promoter, an At3g17520 promoter, an At4g09600 promoter, an AT1G15125 promoter, an AT1G13300 promoter, an AT2G48080 promoter, an AT3G25790 promoter, an AT5G10210 promoter, and an AT5G19970 promoter.
 5. The method of claim 1, wherein the transgenic cell further comprises a polynucleotide sequence that encodes an additional DNA sequence-specific transactivator, wherein transcription of the polynucleotide sequence encoding the additional DNA-sequence-specific transactivator is under the control of a promoter sequence that is recognized by the first DNA-sequence-specific transactivator; and wherein the additional DNA-sequence-specific transactivator regulates transcription of the reporter gene through binding of its cognate sequence that is operably linked to the reporter polynucleotide.
 6. The method of claim 1 further comprising the step of: (c) contacting a plant with the selected compound and detecting a modified trait in the plant relative to controls.
 7. The method of claim 6, wherein the modified trait is selected from the group of increased desiccation or drought tolerance, increased nitrogen use efficiency, and increased disease resistance. 